Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first embodiment of a display screen orportion thereof with a graphical user interface showing the new design;and,

FIG. 2 is a front view of a second embodiment thereof.

The broken lines shown in the figures represent portions of the displayscreen or portion thereof with a graphical user interface that form nopart of the claimed design.

CLAIM I claim the ornamental design for a display screen or portionthereof with a graphical user interface, as shown and described.